(a) Field of the Invention
The present invention relates to a process for preparing 6,6'-dihydroxy-3,3,3',3'-tetramethyl-1,1'-spirobiindane (hereinafter referred to as SPI) and an adduct of SPI with phenol. More particularly, it relates to (A) a process for preparing SPI of high purity by cooling a phenol solution of SPI prepared, for example, by heating 2,2-bis(4-hydroxyphenyl)propane (hereinafter referred to as bisphenol A) in the presence of an acid catalyst or by dissolving crude SPI crystals into phenol, to obtain SPI crystals, and (B) a process for preparing SPI of high purity by cooling the phenol solution of SPI to obtain an adduct of SPI with phenol, and removing phenol from the adduct.
(b) Description of the Prior Art
Known processes for preparing SPI are as follows:
(1) a process which comprises treating bisphenol A in the presence of water in sulfuric acid at a temperature of 140.degree. C. and carrying out fractional crystallization from an organic solvent such as toluene to prepare SPI (U.S. Pat. No. 3,271,463); PA1 (2) a process which comprises treating bisphenol A with concentrated hydrochloric acid in the presence of water at a temperature of 100.degree. C. in an autoclave and carrying out fractional crystallization from an organic solvent such as toluene to prepare SPI (U.S. Pat. No. 3,271,463); PA1 (3) a process which comprises heating bisphenol A in hydrobromic acid (Journal of Chemical Society, p415, 1962);and PA1 (4) a process which comprises heating bisphenol A in the presence of a perfluoroalkanesulfonic acid, an aliphatic sulfonic acid or an ultrastrongly acidic resin (JP-A-62-10030, JP-A-62-42941 and JP-A-62-4239).
However, the abovementioned processes are disadvantageous from a viewpoint that SPI crystals obtained are not as good as they are expected in purity and the crystals are needed to further purify. For examples, chloroform washing, converting SPI into a disodium salt of it, followed by four times of recrystallization, further converting the salt into free SPI and furthermore one time of recrystallization are needed in the purification step (journal of polymer Science: Part A by Stueben, Vol.3, pp3,209-3217, 1965).
Moreover, a method is known which comprises heating bisphenol A with methanesulfonic acid catalyst to obtain a reaction mixture, putting the reaction mixture into water to obtain a precipitate, washing the precipitate with methylene chloride, dissolving the precipitate in a mixed solvent containing methanol and methylene chloride, adding water into the solution to obtain a precipitate, and repeating the abovementioned treatments several times (JP-A-63-146837). In this method, a lot of solvents are used, the step for preparing SPI is large in number and its operation is complex.